Decoding shellcode gets detected in memory on runtime

Question

I am developing a custom shellcode encoder in C++. It takes shellcode as a command line argument and generates encoded shellcode (unsigned char array) and the instructions to decode it (C/C++ code). I then use the output of my encoder into a C process injection template for Windows. With the original shellcode being an msfvenom windows/x64/shell_reverse_tcp payload and Windows defender turned off, everything works fine (program completes without errors, I get a reverse shell). But with defender on, the decoded shellcode in memory is detected as a "meterpreter" payload right after the decode routine completes. What is the correct way to handle the decoded shellcode in memory to avoid detection? I've tried storing the decoded shellcode in an unsigned char array defined on the stack, heap as well as writing each decoded byte with WriteProcessMemory(hProcess, shellcodeAddr+i, &decoded_byte, 1, NULL); using a loop.